CN111025665B - Time shaper - Google Patents
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- CN111025665B CN111025665B CN201911386667.9A CN201911386667A CN111025665B CN 111025665 B CN111025665 B CN 111025665B CN 201911386667 A CN201911386667 A CN 201911386667A CN 111025665 B CN111025665 B CN 111025665B
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/09—Beam shaping, e.g. changing the cross-sectional area, not otherwise provided for
- G02B27/0938—Using specific optical elements
- G02B27/0977—Reflective elements
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/09—Beam shaping, e.g. changing the cross-sectional area, not otherwise provided for
- G02B27/0938—Using specific optical elements
- G02B27/095—Refractive optical elements
- G02B27/0972—Prisms
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/10—Beam splitting or combining systems
Abstract
The invention provides a time shaper which is high in conversion efficiency, low in cost, simple in structure and easy to install and adjust, and aims to solve the technical problems that the existing 4F structure-based femtosecond laser pulse time shaper is low in conversion efficiency, extremely expensive in price and difficult to install and adjust, and the requirement of the femtosecond pulse time shaper on spatial postures of a beam combining mirror, a beam splitter and the like is extremely high and the installation and adjustment is difficult. Different from the traditional scheme for generating the optical path difference, the optical path difference is generated based on the difference between the refractive indexes of the optical element material and air, no moving device is arranged in the whole device, and the prism which is easy to install and adjust is adopted, so that the beam combination precision can be effectively ensured, the requirement on the space posture of the reflector is lower, and the installation and the adjustment are more convenient. Because the invention only has the transmittance attenuation among the optical elements, the loss of light energy is small, and the utilization rate of the light energy can reach more than 90 percent.
Description
Technical Field
The invention relates to the technical field of femtosecond laser pulse shaping, in particular to a time shaper.
Background
In various industries such as silicon processing, Integrated Circuit (IC) back-end processing, microelectronic packaging, solar energy manufacturing, and the like, as the wafer thickness is continuously reduced, the brittle material processing faces a serious challenge, and higher requirements are provided for the manufacturing precision (scribe line width) and quality (edge breakage, roughness, and the like) of the brittle material, and the emergence of a femtosecond laser pulse shaping technology is promoted. The time shaping is to shape one laser pulse into several sub-pulses, and the time delay between sub-pulses, the number of sub-pulses and the energy of the sub-pulses can be shaped according to actual needs. The femtosecond laser pulse after time shaping can more flexibly and more deeply influence the processes of material phase change and the like, thereby providing more convenience for realizing high-precision, high-quality and high-efficiency material processing, and particularly having obvious advantages in the aspects of precision drilling, scribing, cutting (such as glass and silicon wafer cutting) and marking.
As shown in fig. 1, an existing femtosecond laser pulse time shaper is mainly a 4F time shaper, an incident femtosecond laser pulse irradiates a first grating 101 at a certain angle, dispersion is generated in a transverse direction, laser with different frequency components is incident on a cylindrical mirror at different diffraction angles, and since the distance from the center of the grating to the center of a first lens 102 is F, the incident laser passes through the first grating 101 and the first lens 102, fourier transform from a time domain to a frequency domain is realized, and light with different frequency components is distributed in sequence in space. The phase plate 103 located in the focal plane of the first lens 102 can independently modulate light with different frequency components, and the adjustable quantity includes phase, amplitude and polarization. The laser passing through the phase plate 103 is incident on the second lens 104 and then focused on the second grating 105, and is compressed by the second grating 105 and then emitted, so that the conversion from the frequency domain to the time domain is realized. Generally, the dielectric material used for such a phase plate 103 is generally a material whose refractive index is significantly influenced by light or phonons, and the control accuracy of the pulse delay depends on the control accuracy of the voltage. The 4F time shaper has advantages in the aspects of control precision of pulse delay, suppression of high-order dispersion, alignment of processing light spots and the like, but has obvious disadvantages: low conversion efficiency (only about 60%), poor sub-pulse energy/polarization regulation and control capability, small regulation and control range of pulse delay and extremely high price (the price is about eighty thousand). This causes difficulties for the processing of some important transparent materials, because the processing threshold of transparent materials is high; furthermore, the small pulse delay provided greatly limits the ability of the femtosecond laser to process hard, brittle and transparent materials.
At present, another femtosecond laser pulse time shaper based on an optical path difference principle is provided, wherein laser is divided into two paths of light beams, then a reflector on a light path is adjusted, so that the two paths of light beams generate different optical path differences, and finally the light beams are combined to realize time shaping; the method has high energy utilization rate, the generated pulse delay can be adjusted, but only two sub-pulses can be generated, the requirements on spatial postures of a beam combiner, a spectroscope and the like are extremely high, and the installation and adjustment are very difficult.
Disclosure of Invention
The invention provides a time shaper which is high in conversion efficiency, low in cost, simple in structure and easy to install and adjust, and aims to solve the technical problems that the existing 4F structure-based femtosecond laser pulse time shaper is low in conversion efficiency, extremely expensive in price and difficult to install and adjust, and the requirement of the femtosecond pulse time shaper on spatial postures of a beam combining mirror, a beam splitter and the like is extremely high and the installation and adjustment is difficult.
The technical scheme of the invention is as follows:
a time shaper, characterized by: comprises a prism group, a reflecting mirror and a beam combining mirror group;
the prism group comprises a first prism, a second prism, … and an Nth prism; the first prism, the second prism, … and the N-1 prism are all plated with light splitting films; n is more than or equal to 2;
the beam combining mirror group comprises a first beam combining mirror … and an N-1 beam combining mirror; the first beam combiner, … and the N-1 beam combiner are respectively plated with a light splitting film;
the second prism, …, the Nth prism is set up in the reflected light path of the said first prism sequentially, the reflecting mirror is set up in the transmitted light path of the first prism; or the second prism, … and the Nth prism are sequentially arranged on the transmission light path of the first prism, and the reflecting mirror is arranged on the reflection light path of the first prism;
the first beam combiner, … and the N-1 beam combiner are sequentially arranged on the reflection light path of the reflecting mirror and are respectively positioned on the reflection light paths of the second prism, … and the N prism.
Further, defining the transmitted light beam of the first prism as a first sub-pulse, the reflected light beam of the first prism as a second sub-pulse, and arranging a diaphragm on the propagation path of the first sub-pulse and/or the second sub-pulse; n is 2.
Or, defining the transmitted beam of the first prism as a first sub-pulse, the reflected beam of the first prism as a second sub-pulse, the transmitted beam of the second prism as a third sub-pulse …, and the transmitted beam of the N-1 th prism as a N sub-pulse; n is more than or equal to 3;
diaphragms are respectively arranged on the propagation paths of the sub-pulse I, the sub-pulse II and the sub-pulse III …; alternatively, diaphragms may be provided in propagation paths of one or more of the first sub-pulse, the second sub-pulse …, and the N sub-pulse.
Further, the first prism, the second prism, …, the nth prism are all isosceles prisms.
Further, the first prism, the second prism, …, the nth prism are equal or unequal in size.
Furthermore, the first prism, the second prism, … and the Nth prism are made of the same material.
Further, the diaphragm is an electrically controlled variable diaphragm.
The invention has the advantages that:
1. high energy conversion efficiency
Because the invention only has the transmittance attenuation among the optical elements, the light energy loss is small, and the light energy utilization rate (namely the conversion efficiency) can reach more than 90 percent.
2. Low cost
The invention has simple structure, low cost and easy realization, and is beneficial to practical application.
3. Easy to be installed and adjusted
Different from the traditional scheme for generating the optical path difference, the optical path difference is generated based on the difference between the refractive indexes of the optical element material and air, no moving device is arranged in the whole device, and the prism which is easy to install and adjust is adopted, so that the beam combination precision can be effectively ensured, the requirement on the space posture of the reflector is lower, and the installation and the adjustment are more convenient.
4. Easily ensure the beam combination precision
Aiming at the problems that the beam splitting ratio and the roundness of a focusing light spot are caused by various errors existing between the beam splitting and beam combining, such as angle errors between the normal direction of a spectroscope and incident light, the energy ratio of two or more sub-pulses has larger deviation with 1:1, or the space characteristics of the two sub-pulses are inconsistent (one is circular and the other is elliptical), a prism which is easy to install and adjust is adopted, so that the beams are easy to combine;
5. simplifying the modulation of energy between sub-pulses
The energy modulation among the sub-pulse sequences can be flexibly realized by adjusting the electric control variable diaphragm, and/or the modulation of the energy ratio of the sub-pulse sequences is realized by carrying out film layer proportion design on the light splitting surface of the prism.
6. Can generate two or more sub-pulses, can meet the actual requirement of laser processing, broadens the laser processing capability and is beneficial to improving the quality and the efficiency of ultrafast laser processing.
7. The time shaping precision is high
Compared with the traditional scheme of generating optical path difference by utilizing the adjusting reflector, the prism has higher precision of the reference surface, so that the assembly and adjustment precision is higher, and the precision of the whole time shaper is higher.
Drawings
Fig. 1 is a schematic diagram of a conventional 4F time shaper.
Fig. 2 is a schematic diagram of an embodiment of the present invention.
Description of reference numerals:
101-a first grating, 102-a first lens, 103-a phase plate, 104-a second lens, 105-a second grating;
201-first isosceles prism, 202-second isosceles prism, 203-third isosceles prism, 204-first diaphragm, 205-second diaphragm, 206-reflector, 207-first beam combiner, 208-second beam combiner, 209-first sub-pulse, 210-second sub-pulse and 211-third sub-pulse.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
As shown in fig. 2, the time shaper of the present invention realizes time shaping based on the principle of optical path difference, and is mainly composed of an isosceles prism group, a diaphragm group, a mirror group, etc., wherein the optical path difference is mainly realized by the isosceles prism group in the optical path (the number of the isosceles prisms depends on the system need to generate several sub-pulses), and the energy ratio between the sub-pulses is realized by an electrically controlled iris diaphragm.
Example 1:
the present embodiment is capable of generating two sub-pulses, which constitute the optical path shown by the solid line portion in fig. 2, and includes a first isosceles prism 201; ultrafast laser pulse output by the femtosecond laser is divided into two paths after being incident to the first isosceles prism 201: a first diaphragm 204 and a reflecting mirror 206 are sequentially arranged on the optical path (namely, a transmission optical path) of the sub-pulse one 209; a second diaphragm 205 and a second isosceles prism 202 are sequentially arranged on the optical path (i.e. the reflection optical path) of the second sub-pulse 210;
a first beam combiner 207 is arranged at the intersection of the reflection light path of the first sub-pulse 209 reflected by the reflector 206 and the reflection light path of the first sub-pulse 210 reflected by the second isosceles prism 202;
the incidence surfaces of the first isosceles prism 201 and the first beam combiner 207 are both provided with a semi-transparent and semi-reflective film (the splitting ratio is 1: 1).
The half waist lengths of the first isosceles prism 201 and the second isosceles prism 202 are equal and are all marked as L; the refractive indexes of the first isosceles prism 201 and the second isosceles prism 202 are equal to the refractive index of air, and the difference is denoted as Δ n.
An ultrafast laser pulse output by the femtosecond laser enters the first isosceles prism 201 and is divided into a first sub-pulse 209 and a second sub-pulse 210 with equal energy (when the splitting ratio is 1:1), and a general calculation formula of an optical path difference and a time delay between an optical path of the second sub-pulse 210 and an optical path of the first sub-pulse 209 is as follows: the optical path difference delta s is delta n multiplied by L, and the time delay delta t is delta s/c; c is the speed of light; l is the propagation path length of the light.
If n is1Is the refractive index of air, n2Is the refractive index of a single isosceles prism, d is the thickness of a single mirror, n3Is the refractive index of the individual mirrors, and c is the speed of light. The time delay of sub-pulse two 210 and sub-pulse one 209 is: [ (n)2-n1)L1+n2L2/2-n3d/0.707]/c。
The first sub-pulse 209 is reflected by the mirror 206 and then enters the first beam combiner 207, the second sub-pulse 210 is reflected by the second isosceles prism 202 and then enters the first beam combiner 207, and the first beam combiner 207 can combine and output the first sub-pulse 209 and the second sub-pulse 210 due to the fact that the first beam combiner 207 is plated with the semi-transparent and semi-reflective film, and therefore the ultrafast sub-laser pulse sequence formed by the first sub-pulse 209 and the second sub-pulse 210 with any energy ratio and time interval delta t is obtained.
If the energy ratio between the sub-pulse one 209 and the sub-pulse two 210 is adjusted, the adjustment can be realized by adjusting the first diaphragm 204 and/or the second diaphragm 205; the first aperture 204 and the second aperture 205 are preferably electronically controlled variable apertures.
Example 2:
as shown in the whole optical path (solid line + dotted line portion) in fig. 2, in order to generate three sub-pulses, a transflective film may be plated on the reflective surface of the second isosceles prism 202, so that the second sub-pulse 210 is transmitted through the second isosceles prism 202 to obtain a third sub-pulse 211, and a third isosceles prism 203 is further disposed on the optical path of the third sub-pulse 211; a second beam combiner 208 is further arranged at the intersection of the reflection light path of the third sub-pulse 211 reflected by the third isosceles prism 203 and the reflection light path of the second sub-pulse 210 reflected by the first beam combiner 207.
The incidence plane of the second beam combiner 208 is coated with a transflective film.
The third isosceles prism 203 has the same half waist length as the first isosceles prism 201 and the second isosceles prism 202, which is also L; the difference between the refractive index of the third isosceles prism 203 and the refractive index of air is also Δ n.
The first sub-pulse 209 is reflected by the mirror 206 and then enters the first beam combiner 207, and the second sub-pulse 210 is reflected by the second isosceles right prism 202 and then enters the first beam combiner 207, because the first beam combiner 207 is provided with a semi-transparent and semi-reflective film;
a part of the first sub-pulse 209 is transmitted by the first beam combiner 207 and then reflected by the second beam combiner 208; part of the second sub-pulse 210 is reflected by the first beam combiner 207 and then reflected by the second beam combiner 208; the third sub-pulse 211 is reflected by the third isosceles prism 203 and then transmitted by the second beam combiner 208; thus, the second beam combiner 208 realizes beam combination output of the first sub-pulse 209, the second sub-pulse 210 and the third sub-pulse 211, and obtains an ultrafast sub-laser pulse sequence composed of the first sub-pulse 209, the second sub-pulse 210 and the third sub-pulse 211.
If n is1Is the refractive index of air, n2Is the refractive index of a single isosceles prism, d is the thickness of a single mirror, and c is the speed of light. The time delay between sub-pulse two 210 and sub-pulse one 209 is: [ (n)2-n1)L1+n2L2/2-n3d/0.707]And c, the time delay of the sub-pulse three 211 and the sub-pulse two 210 is as follows: [ (n)2-n1)L1/2-n3d/0.707]/c。
To adjust the energy ratio, a third diaphragm (not shown) may be disposed in the propagation path of the sub-pulse three 211, and the third diaphragm may be located between the second isosceles prism 202 and the third isosceles prism 203, or between the third isosceles prism 203 and the second combiner 208.
In practical application, the above embodiments 1 and 2 can be utilized, and so on, to realize > 3 sub-pulses.
Claims (7)
1. A time shaper, characterized by: comprises a prism group, a reflecting mirror and a beam combining mirror group;
the prism group comprises a first prism, a second prism, … and an Nth prism; the first prism, the second prism, … and the N-1 prism are all plated with light splitting films; n is more than or equal to 2;
the beam combining mirror group comprises a first beam combining mirror … and an N-1 beam combining mirror; the first beam combiner, … and the N-1 beam combiner are respectively plated with a light splitting film;
the second prism, …, the Nth prism is set up in the reflected light path of the said first prism sequentially, the reflecting mirror is set up in the transmitted light path of the first prism; or the second prism, … and the Nth prism are sequentially arranged on the transmission light path of the first prism, and the reflecting mirror is arranged on the reflection light path of the first prism;
the first beam combiner, … and the N-1 beam combiner are sequentially arranged on the reflection light path of the reflecting mirror and are respectively positioned on the reflection light paths of the second prism, … and the N prism.
2. The time shaper of claim 1, wherein: defining a transmitted light beam of the first prism as a first sub-pulse, a reflected light beam of the first prism as a second sub-pulse, and arranging a diaphragm on a propagation path of the first sub-pulse and/or the second sub-pulse; n is 2.
3. The time shaper of claim 1, wherein: defining the transmitted beam of the first prism as a first sub-pulse, the reflected beam of the first prism as a second sub-pulse, the transmitted beam of the second prism as a third sub-pulse …, and the transmitted beam of the N-1 th prism as a N sub-pulse; n is more than or equal to 3;
diaphragms are respectively arranged on the propagation paths of the sub-pulse I, the sub-pulse II and the sub-pulse III …; alternatively, diaphragms may be provided in propagation paths of one or more of the first sub-pulse, the second sub-pulse …, and the N sub-pulse.
4. A time shaper according to any of claims 1-3, wherein: the first prism, the second prism, …, the Nth prism are all isosceles prisms.
5. The time shaper of claim 4, wherein: the first prism, the second prism, …, the nth prism are equal or unequal in size.
6. The time shaper of claim 5, wherein: the first prism, the second prism, …, the Nth prism material is the same.
7. The time shaper of claim 2 or 3, wherein: the diaphragm is an electrically controlled variable diaphragm.
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| CN201911386667.9A CN111025665B (en) | 2019-12-29 | 2019-12-29 | Time shaper |
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| CN201911386667.9A CN111025665B (en) | 2019-12-29 | 2019-12-29 | Time shaper |
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| KR100804425B1 (en) * | 2006-10-02 | 2008-02-20 | (주)미래컴퍼니 | Apparatus and method for controlling laser pulse |
| EP2264839A2 (en) * | 2009-06-18 | 2010-12-22 | Raytheon Company | LCD based polarization, phase and amplitude spatial light modulator. |
| CN202649600U (en) * | 2012-05-17 | 2013-01-02 | 西安理工大学 | Time-domain optical pulse shaping device |
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